Electric machines convert energy through electromagnetic interactions, such as electricity to electricity (transformer), electricity to mechanical power (motor), or mechanical power to electricity (generator). A factor that influences the energy conversion is the magnetic core materials, which are generally formed from laminations of electric steels (also called silicon steel). In addition to electric machines, magnetic cores in inductors also play a role in their performance. However, core loss (also called iron loss) in the magnetic core occurs due to the AC magnetic field inside the materials, especially during high frequency operation. Core loss generally includes three components: hysteresis loss, eddy current loss and excess loss (or anomalous loss). Hysteresis loss is frequency independent, while both eddy-current and excess losses are frequency dependent.
As fuel economy is an important factor in electric vehicles (EVs), such as hybrid electric vehicles (HEVs), plug-in hybrid EVs (PHEVs), and battery EVs (BEVs), reducing core loss and increasing induction (flux density) in the magnetic cores (such as rotor and stator cores) of electric machines and power electronics (such as inductor cores) may be a goal. Conventional core forming processes generally reduce losses by sacrificing other magnetic properties or enhance magnetic properties such as flux density but sacrifice loss performance.
One common way to reduce core loss in a magnetic core is to reduce the lamination thickness of the electric steel through mechanical rolling, including hot and cold rolling. Magnetic cores with thinner laminations have significantly lower eddy-current loss, and therefore lower core loss, than thicker laminations. Another way to reduce core loss is to control the chemical composition in electric steels, e.g., Si and Al content. Since Si and Al increase resistivity in electric steels, they are generally controlled during manufacturing in order to reduce the eddy-current loss. Usually 2-3% Si is used in non-oriented electric steel and about 6% in grain-oriented electric steel. Although core loss is significantly reduced by these two approaches, it is still problematic, especially for high frequency applications. Another approach to reduce core loss is to produce magnetic powders that are sintered into a bulk core directly, with or without an insulating coating on the magnetic particles. A similar approach is to mix magnetic powders with a binder and then press them into near-shape devices. However, the use of a binder may reduce the flux density and permeability of the core.